Field of the Invention
The invention relates to a separating device for precipitating solid particles from a gas flow of a combustion chamber or circulating fluidized-bed or CFB reactor, wherein the gas flow carries the particles along and a device influences the gas flow in such a way that centrifugal and gravitational forces which are greater than entraining forces of the gas flow act on the solid particles and thus permit particles of a specific minimum size to be separated from the gas flow.
A CFB system operates by using a circulating fluidized-bed reactor. In that case, primary air flows from bottom to top through a mass composed of fine-grained, solid particles which are fed to a combustion chamber. When the fluidized bed is formed, a force due to the weight of the solid particles is canceled by an opposing force of the gas flow.
A portion of the solid particles leaves the fluidized-bed reactor with the gas flow. The solid particles are removed from the gas flow by additional devices, in order to ensure a solids cycle which is required for the process.
It is known to use centrifugal-force precipitators referred to as cyclones to separate the solid particles from the exhaust gas flow. The principle of centrifugal-force precipitation is based on the action of centrifugal forces. Centrifugal forces which are produced by accelerating the gas/solids mixture onto a circular track around the vertical cyclone axis act with different strengths on the gas component and solids component of the gas flow. The centrifugal force increases with increasing particle size, with the result that the particles are precipitated starting from a specific grain size. Particles which are smaller than the so-called separating grain follow the gas flow. The solid particles which are larger than the separating grain of the cyclone are flung against its wall and slide downwards to a solids outlet. The gas flow and the solid particles which are smaller than the separating grain leave the cyclone through a central opening in the ceiling.
Particularly in the case of cyclones in which the gas flow is very heavily loaded with solids, the effect of the centrifugal-force precipitation is very strongly overlaid by mass precipitation, that is to say a large portion of the particles in the gas flow does not swell repeatedly around the vertical cyclone axis but, immediately after entering the cyclone, drops downwards to the solids outlet in the form of a downwardly directed solids tube. Only a relatively small portion of the solid particles is separated from the gas flow by centrifugal force precipitation.
Cyclones of conventional construction for CFB systems are very large, bulky structures which need to have large masses of masonry for the purpose of adequate thermal insulation and to provide protection against erosion by impacting solid particles. Those masses of masonry may only be heated up slowly, which results in long start-up times for CFB systems. Start-up and run-down operations reduce the service life of the outer masonry. Furthermore, expensive compensators are required in the conventional construction of cyclones because of differences in the magnitudes and directions of the thermal expansion for the cyclone, the combustion chamber and a boiler convection section.